The present invention relates to the diagnostic imaging arts. It finds particular application in conjunction with contrast agent enhanced angiography such as magnetic resonance and computed tomography angiography and will be described with particular reference thereto. It will be appreciated, however, that the invention is also applicable to other types of magnetic resonance flow imaging and contrast agent enhanced imaging in other modalities.
Magnetic resonance angiography is used to view the blood vessels of the body. Dipoles in the blood of the subject are excited and imaged as they propagate through vessels of interest. A clinician analyzes the images to identify various circulatory abnormalities, such as slow flow points, partial blockages within vessels in the image, complete occlusions, and the like.
In magnetic resonance angiography, the dipoles being imaged are in motion. Advantageously, the dipoles move though an imaging region, traveling along in the bloodstream. Magnetic resonance angiography imaging can be enhanced with a contrast agent, which is injected into the blood. A sequence is selected that shows the contrast agent very well against other tissue in a magnetic resonance image. Thus, it is very useful for viewing the blood vessels of the body.
Most often, the contrast agent is injected into a region of the subject outside the imaged region. The injected contrast agent, or bolus, travels in the bloodstream for a period of time before it reaches the imaging region. Timing the arrival of the bolus is critical in that there is a small time window in which the contrast agent is at its peak concentration in the examination region, i.e. when the optimum image can be acquired. Multiple factors play a role in the travel time of the bolus, such as position of the region of interest relative to the injection of the contrast agent, subject age, sex, and weight, and vascular anomalies such as obstructions in blood vessels.
Prior methods for estimating the arrival time of the bolus do not adequately predict arrival times for all patients. In a test bolus method, a small amount of contrast agent, that is, a test bolus, is injected into the patient. The region of interest is monitored by taking real-time fluoroscopic images at a rate of about one per second of the region of interest. The time that the test bolus takes to show up in the fluoroscopic images is recorded. A second injection, this time with the full bolus, is administered to the subject. The operator waits the amount of time it took the test bolus to reach the region of interest before initiating a diagnostic scan.
Although simple and straightforward, the test bolus method has drawbacks. In practice, 20-25% of trials run using this method fail to detect the test bolus. If the test bolus is not detected, the operator typically makes a subjective guess based on his/her experience. Additionally, the test bolus method requires an extra injection of contrast agent. This adds to patient discomfort, and the test bolus is partially absorbed as it travels through the region of interest, degrading contrast and definition in the final image. Moreover, the fluoroscopy monitoring for the test bolus has a low temporal resolution, about one frame per second which limits the accuracy of the predicted delay time. Further, the timing parameters of the test bolus may not be the same due to significantly different intravascular bolus concentrations. Patient movement between or during scans can also affect how the test bolus and the real bolus move through the subject.
Other methods include real time tracking of a single, large bolus. One full strength injection is given to the patient, and the examination is monitored for the arrival of the contrast agent. One method of tracking the bolus involves repeatedly monitoring a single line of k-space for magnetic resonance signal intensity changes. In k-space, the intensity of the signal spikes when the region of interest receives the bolus. Problems with this method include a lack of a base image, and sensitivity to physical motion. Because the tracking signal does not generate images, the operator cannot see the traveling bolus and must rely solely on the machine or intuition to make the decision to start imaging. Movement can also affect this method. Slight movement during the scan can falsely trigger a diagnostic image. For example, moving fat dipoles into the monitored region of interest causes the signal intensity to rise.
Real time fluoroscopic images can be used without the a bolus. In this method, the operator watches the fluoroscopic images, when he/she thinks the bolus has arrived, the diagnostic image data acquisition is initiated by the operator. Drawbacks to this method include its low temporal resolution and subjective triggering. Typically, temporal resolution is on the order of one frame per second. However, temporal resolution can be reduced at the expense of image quality.
Another method is the TRICKS method which samples the center of k-space more frequently than other portions of k-space. Resultantly, the probability of catching the plateau period of the signal increases. However, undersampling of the non-central portions of k-space means loss of high and middle frequency information. This method can be thought of as a xe2x80x9cblindxe2x80x9d oversampling of center k-space, as it is not guaranteed to catch the plateau period, and can miss the bolus entirely.
The present invention provides a new and improved method and apparatus which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method of angiographic imaging is provided. A region of interest of a subject is disposed in an examination region. Physical parameters of the subject are entered into a parameter database. Triggering information is calculated from previously entered information to the parameter database. A contrast agent is injected into the patient and monitoring for the arrival of the contrast agent to a region of interest is commenced. A diagnostic imaging scan is initiated in response to the arrival of the contrast agent and the parameter database is updated.
In accordance with another aspect of the present invention, a method of diagnosing vascular anomalies is provided. A subject is injected with a contrast agent. Angiographic images are generated of a region of interest of the subject. Times tD, tA, and tV are measured and compared to a database that includes recorded times tD, tA, and tV of a multiplicity of patients.
In accordance with another aspect of the present invention, a diagnostic imaging apparatus is provided. A parameter compilation memory stores contrast agent uptake times from a plurality of prior scans of other subjects. A contrast agent detection circuit verifies successful detection of the agent and loads the uptake times into the parameter compilation memory. A reconstruction processor reconstructs received data signals into an image representation of the subject.
In accordance with another aspect of the present invention, a diagnostic imaging apparatus is provided. The apparatus includes a means for generating contrast agent enhanced diagnostic images, a parameter memory, a means for determining the contrast agent related parameters, a means for comparing the parameters, and a means for analyzing the parameters.
In accordance with another aspect of the present invention, an angiographic imaging apparatus is provided. The apparatus includes a means for generating contrast agent enhanced diagnostic images, a means for monitoring contrast agent arrivals, a memory means that stores arrival time of past patients and past patient physiological characteristics, and a means for determining a projected arrival window.
One advantage of the present invention resides in more robust bolus detection.
Another advantage resides in an accumulation of knowledge and the use of the knowledge to improve future scans.
Another advantage resides in the ability to search for vascular anomalies prior to generating a magnetic resonance angiography image.
Another advantage resides in the ability to perform a clinical diagnosis based on detected imaging parameters related withe physiological conditions or changes in a patient.
Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.